The present invention relates to the field of zirconium oxide oxygen sensors and particularly to a low cost, integratable absolute O.sub.2 sensor apparatus. The present design is directed to minimize the heater power required to heat the ZrO.sub.2 to operating temperature, to be adaptable for use with low voltage IC's, and to utilize only small amounts of noble metal electrodes while giving fast response time at low cost.
One type of electrode-active oxygen monitor is shown in the de Bruin et al U.S. Pat. No. 4,326,318 which discloses an electrolytic cell including an electrode of platinum and palladium, and an electrolyte of yttrium stabilized zirconia.
A gas detector for another gas such as CO or chlorine is shown in the Kimura U.S. Pat. No. 4,343,768, titled "Gas Detector," in which a recess is formed in a substrate below an upper film of electrically insulating substance.
Another oxygen sensor is taught in the Takao et al U.S. Pat. No. 4,107,019 titled "Solid Electrolyte Thin Film Oxygen Sensor Having Thin Film Heater." In this patent a ceramic substrate having a heater embedded in the substrate has on the surface of the substrate a sandwich construction of an electrically conductive film (partially oxidized metal), a layer of zirconium oxide electrolyte, and a surface metal usually of the platinum group metals.
In an embodiment of the present invention a silicon substrate has a SiO.sub.2 layer formed thereon, the substrate having a depression in a main planar surface which depression is bridged over by the SiO.sub.2 layer so that a hollow exists beneath a bridge portion of the SiO.sub.2. The SiO.sub.2 layer has embedded therein in the region of the bridging area a thin film conductive heater. Formed over the surface of the SiO.sub.2 layer, particularly over the bridge area, is a solid electrolyte layer of zirconium oxide (ZrO.sub.2) which has on the surface a pair of spaced electrodes of a noble metal such as palladium. The electrodes and the heater each have contacts adapted to be connected to an energizing and measuring circuit.